In general, a reciprocating compressor is designed to form a compression space to/from which an operation gas is sucked/discharged between a piston and a cylinder, and the piston linearly reciprocates inside the cylinder to compress refrigerants.
Most reciprocating compressors today have a component like a crankshaft to convert a rotation force of a drive motor into a linear reciprocating drive force for the piston, but a problem arises in a great mechanical loss by such motion conversion. To solve the problem, development of linear compressors is still under progress.
Linear compressors have a piston that is connected directly to a linearly reciprocating linear motor, so there is no mechanical loss by the motion conversion, thereby not only enhancing compression efficiency but also simplifying the overall structure. Moreover, since their operation is controlled by controlling an input power to a linear motor, they are much less noisy as compared to other compressors, which is why linear compressors are widely used in indoor home appliances such as a refrigerator.
FIG. 1 illustrates one example of a linear compressor in accordance with a prior art. The linear compressor has an elastically supported structure inside a shell (not shown), the structure including a frame 1, a cylinder 2, a piston 3, a suction valve 4, a discharge valve assembly 5, a linear motor 6, a motor cover 7, a supporter 8, a body cover 9, mainsprings S1 and S2, a muffler assembly 10, and a mass member 20.
The cylinder 2 is insertedly fixed to the frame 1, and the discharge assembly 5 constituted by a discharge valve 5a, a discharge cap 5b, and a discharge valve spring 5c is installed to cover one end of the cylinder 2. The piston 3 is inserted into the cylinder 2, and the suction valve 4 which is very thin is installed to open or close a suction port 3a of the piston 2.
The linear motor 6 is installed in a manner that a permanent magnet 6c linearly reciprocates while maintaining the gap between an inner stator 6a and an outer stator 6b. To be more specific, the permanent magnet 6c is connected to the piston 3 with a connecting member 6d, and an interactive electromagnetic force between the inner stator 6a, the outer stator 6b, and the permanent magnet 6c makes the permanent magnet 6c linearly reciprocating to actuate the piston 3.
The motor cover 7 supports the outer stator 6b in an axial direction to fix the outer stator 6b and is bolted to the frame 1. The body cover 9 is coupled to the motor cover 7, and between the motor cover 7 and the body cover 9 there is the supporter 8 that is connected to the other end of the piston 3, while being elastically supported in an axial direction by the mainsprings S1 and S2. The muffler assembly 10 for sucking in refrigerant is also fastened to the supporter 8.
Here, the mainsprings S1 and S2 consist of four front springs S1 and four rear springs S2 that are arranged in horizontally and vertically symmetrical positions about the supporter 8. As the linear motor 6 starts running, the front springs S1 and the rear springs S2 move in opposite directions and buff the piston 3 and the supporter 8. In addition to these springs, the refrigerant in the compression space P functions as sort of a gas spring to buff the piston 3 and the supporter 8.
Therefore, when the linear motor 6 starts running, the piston and the muffler assembly 10 connected to it move in a linear reciprocating direction, and with the varying pressure in the compression space P the operation of the suction valve 4 and the discharge valve assembly 5 are automatically regulated. Under this mechanism, the refrigerant flows via a suction pipe on the side of the shell, an opening of the body cover 9, the muffler assembly 10, and suction ports 3a of the piston 3 until it is sucked in the compression space P and compressed. The compressed refrigerant then escapes to the outside through the discharge cap 5b, the loop pipe and an outlet duct on the side of the shell.
FIG. 2 illustrates one example of a mass member installation structure for a linear compressor in accordance with a prior art. As one example, a mass member 20 is fastened with a piston 3, a muffler assembly 10, and a supporter 8 by bolts B. The piston 3 is provided with suction ports 3a at a closed end, and a radially extending flange 3b with four bolt holes 3h at the other open end. The muffler assembly 10 is inserted in part to the piston 3, and the other part is exposed to the rear side of the supporter 8 to be fastened with the flange 3b of the piston 3 by bolts B. The supporter 8 includes a circular center portion 8a that faces the flange 3b of the piston 3, thereby coupling to the rear side of the flange 3b , and a pair of front and rear supports 8b, 8e, 8d and 8c around the center portion 8a. The mass member 20 takes a nearly annular shape, correspondingly to the flange 3b of the piston 3 and to the center portion 8a of the supporter 8. The mass member 20 also couples to the rear side of the center portion 8a of the supporter 8. To this end, four bolts B are fastened one by one in the direction where the front and rear supports 8b, 8d, 8e, and 8c of the supporter 8 are formed.
FIG. 3 illustrates a detailed view of the mass member in FIG. 2, which is adapted to a linear compressor in accordance with a prior art. Referring to FIG. 2 and FIG. 3, the overall shape of the mass member 20 is annular, the center of which has a hole 21 to receive a muffler assembly 10, and four bolt holes 22a, 22b, 22c, and 22d are formed in the circumferential direction to join with the front and rear supports 8b, 8d, 8e, and 8c of the supporter 8 by bolts B in a one-to-one correspondence. Since the mass member 20 together with the piston 3, the supporter 8, and the muffler assembly 10, constitute sort of a linearly reciprocating movable member, four resistance dissipating holes 23a, 23b, 23c, and 23d are formed between the hole 21 and each of the bolt holes 22a, 22b, 22c, and 22d, so as to lessen the drift resistance during the linear reciprocating motion. Needless to say, the mass member 20 is made in the same annular shape with the center portion 8a of the supporter 8 by cutting a scrap ‘a’ out of a square sheet metal A to form a laminate structure that consists of multilayers of the same shape with various thickness.
The mass member 20 is originally added to increase a total mass of the movable member. Because the movable member in a linear compressor adopts sort of a resonant system that is elastically supported by front/rear mainsprings S1 and S2 (see FIG. 1) and a high-pressure refrigerant gas spring, resonance frequency of the linear compressor needs to match operating frequency of the linear motor 6 (see FIG. 1), which is achieved by adjusting the mass of the movable member with the help of the mass member 20 added to the movable member, instead of adjusting stiffness of easily spreading springs.
However, since the mass member adapted to the conventional linear compressor takes the annular form to be coupled to the circular center portion of the supporter and is given a lot of holes to meet diverse needs, it poses problems in terms of a waste of materials caused by scraping action to obtain an annular mass member out of a square raw material, and low mass despite a high amount of materials being used. Unfortunately though, if the mass member is made thicker to secure a sufficiently large mass as compared with the amount of consumed materials, it would naturally occupy more installation space; while if the mass member is made larger in the radial direction, it not only becomes harder to assemble with a component such as a supporter in the opposite direction, but also creates interference with neighboring components during the operation, thereby impairing the operation reliability.
FIG. 4 and FIG. 5 illustrate one example of a movable member assembly structure adapted to a linear compressor in accordance with a prior art. Here, the movable member is assembled to make a linear reciprocating movement in an axial direction, and includes a piston 3, a connecting member 6d provided with a permanent magnet 6c, a supporter 8, a muffler assembly 10, and a mass member 20. The flange of the piston 3, the connecting member 6d, the supporter 8, the muffler assembly 10, and the mass member 20 each have two bolt holes 3h, 6h, 8h, 10h, and 20h to join with each other by bolts B, and a coupling boss 3a is formed in an axial direction at the internal diameter of the flange of the piston 3 to achieve a smooth fit.
Therefore, the movable member is assembled with a jig Z, and the flange of the piston 3 sealingly fits into a piston holder Z1. A connecting member is settled on the rear side of the piston 3 to make the coupling boss 3a of the piston 3 slid into the inner diameter of the connecting member 6d having the permanent magnet 6c, and then the supporter 8 is settled on the rear side of the connecting member 6d to make the coupling boss 3a of the piston 3 slid into the inner diameter of the supporter 8 and two supports 8a and 8b of the supporter 8 are settled on two supporter holding protrusions Z2 and Z3 at the same time. Moreover, the muffler assembly 10 is settled on the rear side of the supporter 8, and part of the muffler assembly 10 is inserted into the inner diameter of the mass member 20, thereby allowing the mass member 20 to settle on the rear side of the muffler assembly 10. As such, when the piston 3, the connecting member 6d having the permanent magnet 6c, the supporter 8, the muffler assembly 10, and the mass member 20 are all positioned at their proper positions, they are joined together by fastening bolts B into the bolt holes 3h, 6h, 8h, 10h, and 20h, respectively.
However, a problem arises in the conventional linear compressor because the presence of the permanent magnet provided to the connecting member magnetizes its neighboring components such as the piston, the supporter, etc., so it is not easy to assemble such components of the movable member at accurate positions. Although a separate coupling boss could be formed at the inner diameter of the flange of the piston and the connecting member and the supporter could be inserted into the coupling boss of the piston for proper positioning, it is still difficult to make other components such as the muffler assembly and the mass member stay at their positions. Overall, the assembly efficiency is therefore deteriorated.
Moreover, despite the fact that the coupling boss of the piston is required only for assembly of the piston, it is produced by processing with narrow tolerance. This consequently increases material cost and processing cost, thereby contributing to an increase in manufacturing costs.